1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
One problem of an image forming apparatus is that the surface potential of a photosensitive drum (photoreceptor) changes due to various factors, which results in a drop in image quality. For example, if the quantity of laser light emitted from a scanner unit drops, the surface potential of the photosensitive drum may become lower than a desired potential, whereby image quality deteriorates. Here a technique to detect the drop in quantity of laser light based on a transfer current amount is known (Japanese Patent Application Laid-Open No. 2012-155075).
Various factors may cause a drop in the quantity of the laser light. For example, if the image forming apparatus is continuously used in air in which such micro-foreign matter as dust and chemical substances are floating, the foreign matter enters the apparatus main body and adheres to the laser light source and other optical components inside the scanner unit. The deposition of dust on the surface of such optical components as a reflection mirror and an imaging lens of the scanner unit causes a gradual drop in reflectance and transmittance, whereby the quantity of laser light emitted from the scanner unit drops. On the other hand, if foreign matter adheres to an emission point of a laser element, such as a laser diode, the quantity of laser light drops dramatically. Therefore a technique to accurately determine a factor that causes a drop in the quantity of laser light is demanded.
With the foregoing in view, it is an object of the present invention to accurately determine a factor that causes a drop in the quantity of laser light.